Darla and Daniel are now 4. During the summertime, Karen tries to establish a feeding routine for the twins, but they are so picky, she gives them whatever they are willing to eat. For Darla, this ends up being sweet foods, but for Daniel, it's salty foods. Karen discusses this with Mark one night, and he brings up a the tips for establishing healthy eating habits that he learned during his developmental degree. Mark tells Karen that she should try to remember that _ (blank) _ varies, but that there are no _ (blank) _. What are the two tips he provided to Karen?